Heatable vehicle windows are known in the art, and typically include top and bottom conductive bus bars in electrical contact with a transparent conductive coating including an electro conductive layer. The electro conductive layer generates heat when electric current is passed therethrough via the bus bars. In such a manner, snow and ice may be melted from vehicle windows such as windshields, backlites, and/or the like. Windows may also be defogged in such a manner. Moreover, since terminal connections (e.g., via jumper wires) for both bus bars are typically provided at the bottom of the window, this means that bus bar portions have to be provided along a side(s) of the window in order to supply electric current to/from the top bus bar.
U.S. Pat. No. 4,820,902 illustrates that conventional heatable vehicle windows utilize both a top bus bar and a bottom bus bar, wherein side leads of the top bus bar extend upwardly along both the right and left sides of the window in areas where the conductive coating has been deleted. This is sometimes undesirable, as the presence of bus bar portions at both sides of the window can reduce the viewing area of the window and/or reduce the area of the heatable conductive coating since the coating has to be deleted from areas where these side bus bar portions are provided.
In order to overcome the problem(s) relating to U.S. Pat. No. 4,820,902 discussed above, a bus bar may be provided along only one side of the heatable window leading to the top bus bar portion (e.g., see U.S. Pat. No. 3,893,234). However, such an arrangement of the '234 patent is problematic in that in certain situations only a limited amount of current can be carried by the side bus bar portion (i.e., it would be desirable for the side bus bar portion to carry more current to/from the top bus bar portion than the '234 side bus bar portion enables). The result of the '234 structure is that the heatable conductive coating cannot be efficiently heated. This problem becomes even more pronounced with larger vehicle windows to be heated.
It can be seen from the above that there exists a need in the art for a heatable vehicle window which includes a bus bar portion for communicating with the top bus bar portion, which extends up only one side of the vehicle window. In such a window, there exists a need in the art for a bus bar portion design capable of additional current capacity so that a large amount of current can be carried to/from the top bus bar portion along only one side of the window.
U.S. Pat. No. 6,042,932 discloses a braided bus bar which is directly electrically connected to an underlying heatable coating via contact pad(s). Unfortunately, because the braided bus bar is directly connected to the heatable coating, hot spots tend to be generated periodically at different points in the coating where the bus bar is electrically connected thereto. It can be seen that it is not desirable for a braided bus bar to be directly electrically connected to an underlying heatable coating. Moreover, the '932 utilizes braided bus bars on both sides of the window, thereby failing to address and/or recognize the problem(s) discussed above.
U.S. Pat. No. 4,703,328 discloses a heatable vehicle rear window including bus bars provided along both sides thereof for supplying current to an array of cross heating elements. Each bus bar includes a conductive frit strip underlying a single strand copper wire lead that is soldered thereto. Because the '328 patent uses bus bars on both sides of the window, it fails to address of remedy the problems in the art discussed above. Moreover, single strand copper wires are typically not capable of carrying enough current to remedy the problems with the '234 patent discussed above.
In view of the above, it will be appreciated by those skilled in the art that there exists a need for a heatable vehicle window which more efficiently supplies current to a heatable conductive coating thereof. In particular, there exists a need for a bus bar portion design that is capable of supplying an adequate amount of electric current to/from a top bus bar when the bus bar portion is provided along only one of two sides of the heatable window.